Abstract This study describes a set of recommendations to improve the precision of shear and punching shear capacity predictions for one-way slabs under concentrated loads, regardless of the governing failure mechanism, using the ABNT NBR 6118:2014 code provisions. For this purpose, a database of 143 test results was developed, including one-way slabs with different support conditions and loading layouts and that failed by different shear failure mechanisms: one-way shear, punching shear or a mixed mode. The key parameters influencing the load capacity and failure mechanism of these slabs were considered for the proposed recommendations: load position and slab width. Adjustments to the effective shear width definition and shear resisting control perimeter were described. Arching action for loads close to the support was also considered in both one-way shear and punching shear predictions. Considering the whole database and without separation by the failure mechanism, the ratio between tested and predicted resistances with the one-way shear expressions shows an average value of 1.22 and a coefficient of variation of 18.3%. The respective ratio between tested and predicted resistances with the punching shear expressions reached an average ratio of 1.23 with a coefficient of variation of 21.3%. Therefore, the proposed recommendations allow for reaching enhanced levels of precision in assessing the shear and punching shear capacity of one-way slabs under concentrated loads, regardless of the governing failure mechanism of the slabs.

Resumo Este estudo descreve um conjunto de recomendações para melhorar a precisão nas previsões de resistência ao cisalhamento e à punção de lajes unidirecionais sob cargas concentradas, independentemente do mecanismo governante na ruptura, utilizando as disposições da norma ABNT NBR 6118:2014. Para isso, foi organizado um banco de dados com 143 resultados de ensaios, incluindo lajes unidirecionais com diferentes condições de apoio e configurações de carregamento e que apresentaram diferentes mecanismos de ruptura por cisalhamento. Os principais parâmetros que influenciam a capacidade de carga e o mecanismo de ruptura dessas lajes foram considerados nas recomendações propostas. Ajustes para a definição da largura efetiva de cisalhamento e perímetro de controle resistente ao cisalhamento foram descritos. A ação de arqueamento para cargas próximas ao apoio também foi considerada nas previsões de resistência ao cisalhamento unidirecional e ao puncionamento. Considerando todo o banco de dados, a razão entre as resistências testadas e previstas com as expressões de cisalhamento unidirecional apresenta um valor médio de 1.22 e um coeficiente de variação de 18.3%. A respectiva relação entre as resistências testadas e previstas com as expressões de puncionamento atingiu uma relação média de 1.23 com um coeficiente de variação de 21.3%. Portanto, as recomendações propostas permitem alcançar maiores níveis de precisão na previsão da resistência ao cisalhamento e ao puncionamento de lajes unidirecionais sob cargas concentradas, independentemente do mecanismo de ruptura governante das lajes.

Abstract Reinforced concrete pipes are usually designed to attend a three-edged-bearing test (TEBT) using the partial safety factors from building structures. This study presents an alternative approach to designing RC pipes based on simplified reliability analyses. The procedure consists of providing curves of failure probability according to the reinforcement areas used in the pipes. The results indicate that RC pipes with simple reinforcement show a failure probability of around 1% with the most traditional design method, even using the partial safety factors from buildings, due to the higher dispersion of the concrete cover and the use of a single reinforcement layer to satisfy different control sections. Meanwhile, RC pipes with double reinforcement show a significantly lower failure probability as each reinforcement layer is designed to satisfy the bending moments from different control sections and due to the larger pipe thickness. In summary, the large randomness of the reinforcement position increases the failure probability of these members compared to traditional building structures.

This paper presents a study on the compressive behavior of steel fiber-reinforced concrete. In this study, an analytical model for stress-strain curve for steel fiber-reinforced concrete is derived for concretes with strengths of 40 MPa and 60 MPa at the age of 28 days. Those concretes were reinforced with steel fibers with hooked ends 35 mm long and with aspect ratio of 65. The analytical model was compared with some experimental stress-strain curves and with some models reported in technical literature. Also, the accuracy of the proposed stress-strain curve was evaluated by comparison of the area under stress-strain curve. The results showed good agreement between analytical and experimental data and the benefits of the using of fibers in the compressive behavior of concrete.